The present application is directed to an apparatus and method of stabilizing the spine by placement of implants between effected vertebrae which result in fusion of the vertebrae. In particular, the present application is directed to an apparatus and method of improving the stabilization of the implants during the fusion process by linking the implants that are positioned between the same vertebrae together in pairs and also linking the implants to adjacent vertebrae. Still further the apparatus and method provides some pre-loading or twisting of the implants such that the axes of the implants are not parallel, so that the implants are further stabilized relative to their position between the vertebrae and more difficult to inadvertently dislodge. The linking apparatus provides end caps for helping to support the vertebrae against subsidence onto the cages and to resist rotation of the cages.
Many millions of people in the United States alone suffer from some type of spinal injury or disease that effects the spine and especially the discs that are located between adjacent vertebrae of the spine. These discs are necessary to properly position and cushion the vertebrae during the movement. Degeneration, injury or other damage to the disc results in improper alignment of and dysfunction of the vertebrae which often also results in severe pain, the inability to move correctly or to perform certain functions, paralysis and other physical problems which may leave the patient totally incapacitated. Approximately ten percent of the persons who have degeneration or herniation of discs are candidates for surgery to correct the problem. Many different systems have been developed to provide relief to persons having defective discs some of which have been effective and some of which have been relatively ineffective. One of the methods of correcting disc defects has been to properly position the adjacent vertebrae relative to each other and then fuse them together in the proper position or alignment.
Fusing often is best in situations where the discs between the adjacent vertebrae have been either damaged or diseased to such an extent that one or more of the discs no longer functions properly and cannot be preserved by simple procedures such as removal of herniated material and the like.
One particular type of fusion device which requires insertion of an implant having live bone between the vertebrae has grown in substantial popularity in recent years. In this type of implant, two such devices are often inserted in spaced relationship relative to one another between two adjacent vertebrae in the region normally occupied by the defective disc. In order to accomplish this, at least part of the disc is removed or the entire disc is removed (discectomy) and the intervertebral implant devices, often referred to as cages, are inserted in receiving bores. Such implants have exterior walls which are fenestrated, porous or windowed so as to provide multiple openings therethrough. The interior of each of the implants is filled with live bone harvested from another part of the persons body, such as the hip and after implantation, the bone of the vertebrae grows into and joins with the live bone in the implants such that the two adjacent vertebrae and the implant bone grow into a single mass causing a fusion of the two vertebrae so as to hold them in a desired position. While this procedure reduces flexibility of the vertebrae, it significantly reduces pain and/or nerve damage due to collapse, missing or defective discs and, therefore, the benefits outweigh the lost flexibility. This is especially true where the patient would otherwise be immobile.
Applicant, as a spinal surgeon, has found that it is desirable to further stabilize the implants, especially during the period between implantation and the time when stabilizing fusion occurs. Consequently, applicant has developed an apparatus and method of joining a pair of implants that are located between two vertebrae in such a manner as to further stabilize the pair such that they are not as likely to become dislodged at some time before the fusion process is complete or afterward. In addition applicant has found it is desirable to secure implants to vertebrae on opposite sides of the implant and to other implants so as to further improve the stability of those implants. Still further, it has been found desirable to form end caps of the linking structure anterior of the cages to provide additional support to the boney endplate of the vertebrae and also to resist rotation of the cages.
Finally, applicant has found that it is desirable to position the implants such that the central axis of the implants are not parallel to one another prior to joining such that it is more difficult to accidentally remove the implants from bores that receive the implants prior to completion of the fusion process. Yet further applicant has found it desirable to place a slight torque on the implants or preload the implants, such that they are biased against the sides of the bore in opposite directions so as to yet further assist in maintaining the implants between the vertebrae during the fusion process.